Devices have heretofore been provided for securely retaining parked vehicles at a loading dock for the purpose of preventing movement of the vehicle during loading and unloading thereof by dock personnel.
An advantageous releasable locking device for this purpose is disclosed in the Hipp U.S. Pat. No. 4,264,259, issued Apr. 28, 1981. The device of the Hipp patent includes a locking member in the form of a hook which is pivotally supported to be movable from a lower unlocked position to an upper locked position in which it is lockingly engageable with a safety bar of a parked vehicle to hold the parked vehicle against the dock.
As indicated in the Hipp patent, suitable switches may be provided for signalling the condition of the locking device and timers and pushbutton controls may be provided for activating an electrical motor of the device for a time interval of only a short duration, for example, one second, to move the locking member from an inoperative mode to an operative mode, or vice versa. In the practical implementation of use of devices such as shown in the Hipp patent, certain problems may occur especially with regard to safety, more particularly in that the vehicle operators and dock personnel are sometimes not given adequate warning in the event of certain possible malfunctions of the device.